The oscillometric technique for blood pressure measurement was developed long ago, but has only found extensive utility more recently, with the advent of inexpensive integrated circuits and even less expensive microprocessor controlled automated blood pressure monitoring systems. Thus, while indirect, manual oscillometric measurement is described in The Southwestern Veterinarian, Vol. 23, Summer of 1970, No. 4, pp. 289-294, practical oscillometry tends to be found in numerous commercial systems wherein a dedicated microprocessor with stored program control operates by controlling cuff pressure, sensing pressure fluctuations caused by heart beats, and performing the requisite calculations which yield heart rate, mean arterial pressure, and systolic and diastolic pressures. The advent of very large-scale integration portends a change from software systems back to hard wired systems, wherein an entire specially configured machine circuit may be included on but a single chip, but in all events such increasing sophistication and decreasing cost provides further supports for the increasing popularity of automated blood pressure monitors.
Of particular interest with respect to the principles of the present invention are the concepts set forth in U.S. Pat. Nos. 4,360,029 and 4,394,034 to M. Ramsey, III, which are commonly assigned with the instant invention. The Ramsey patents derive from common parentage, the former including apparatus claims and the latter including method claims, their division having been made in response to a restriction requirement during the prosecution. Both patents, however, carry common disclosures of apparatus and methods for artifact rejection in oscillometric systems, which have been in practice in the commercially successful DINAMAP* brand monitors, which are manufactured and marketed by Critikon, Inc., of Tampa, FL, the assignee hereof. In accordance with the Ramsey patents, an inflatable cuff is suitably located on the limb of a patient, and is pumped up to a predetermined pressure. Thereupon, the cuff pressure is reduced in predetermined decrements, at each level of which pressure fluctuations are monitored. These typically consist of a DC voltage with a small superimposed variational component caused by arterial blood pressure pulsations (referred to herein as "oscillatory complexes"). Therefore, after suitable filtering to reject the DC component and to provide amplification, pulse peak amplitudes above a given baseline are measured and stored. As the decrementing continues, the peak amplitudes will normally increase from a lower amount to a relative maximum, and thereafter will decrease. The lowest cuff pressure at which the oscillations have a maximum peak value is representative of mean arterial pressure. Systolic and diastolic pressures may be evaluated either as predetermined fractions of mean arterial pressure, or by more sophisticated methods of direct processing of the oscillatory complexes.
The Ramsey patents devote considerable effort and disclosure to the rejection of artifact data and hence to the derivation of accurate blood pressure data. Indeed, as is apparent from FIG. 2 of the Ramsey patents, the most insubstantial portion of the measurement cycle (denominated "T3") is devoted to the execution of complex detection at the various pressure levels, measurement of signal peaks of true complexes, and processing those peaks in accordance with artifact rejection algorithms so in sequence to identify the pressure level at which the peaks are a relative maximum, that is, mean arterial pressure. As taught by the Ramsey patents, about thirty seconds of a total cycle of less than 40 seconds are devoted to these "T3" functions.
It is a primary object of the principles of the present invention to reduce the time required to proceed through the pressure decrementing steps, correspondingly to provide data more rapidly to the administering physician, and to increase patient comfort by speeding the deflation and decreasing the time at which arterial occlusion takes place. Corespondingly, such improvements in speed and comfort should be had without penalty to overall accuracy.
It is a subsidiary but related object to make such improvements to systems of the class described in the Ramsey patents, with but minimal hardware or software variation, thereby to provide data and performance which is consistent with the considerable mass of clinical data already available for such systems.